In the coming year, arachnoiditis from pantopaque and nonionic aqueous myelographic contrast medium will be measured. The effect of prophylactic intrathecal stenosis may also be studied. The major goal of studies in the coming year will be to determine the sequential morphological changes in the arachnoid following myelography. Animals will be sacrificed at 4,8,12,24,48 & 96 hours following myelography with meglumine iocarmate (1.2 ml, 282 mg I/ml) that is known to produce arachnoiditis in 100% of animals. Electron microscopy, electron dispersal analysis, light microscopy will be performed on the excised arachnoid to evaluate morphologic changes of the arachnoid cells and the development of an inflammatory reaction. Selected specimens will be studied with polarizing light microscopy and immunoflurorescent staining to determine if crystalline contrast medium, or immune complexes are present in the arachnoid. In selected animals, muscle biopsy will be performed to determine if neurogenic muscle atrophy occurs in animals with severe arachnoiditis.